Impeller for centrifugal pulverizer



United States Patent Ofiice 3,346,203 Patented Oct. 10, 1967 3,346,203 IMPELLER FOR CENTRIFUGAL PULVERIZER Ostap Danyluke, Newtown Square, Pa., assiguor to Bath Iron Works Corporation, Bath, Maine, a corporation of Maine Filed July 12, 1965, Ser. No. 471,149 7 Claims. (Cl. 241-275) This invention relates to a centrifugal pulverizer. More specifically, the invention relates to the impeller for projecting outwardly the material fed to the pulverizer. According to my invention, an impeller is provided having certain novel features which improve its operation and life.

As is known, in a typical centrifugal pulverizer of the type involved, there is generally provided an impeller which is driven rotationally about a vertical axis supported and driven at the bottom end and fed at the top end through a circular vertical feed tube at the center. The material being crushed enters at the center of the impeller and by means of vanes is propelled outwardly under the action of centrifugal force, and is discharged at relatively high velocity against either a bed of like material or against breaker plates. The impeller is principally used to accelerate the material, and the reduction of the material is accomplished at the point of impact on the bed or on the breaker plates. An improved impeller of this type is shown and described in my US. Patent 3,162,386, granted December 22, 1964, and assigned to Bath Iron Works Corporation, Bath, Maine.

In operation, it has been found that some of the material that is discharged from the impeller tends to rebound and re-enter the impeller discharge area. The amount of material which rebounds depends more or less upon the clearances between the outer periphery of the impeller and the bed of like material or breaker plates.

Where highly abrasive materials are being pulverized, it is desirable to line or coat the discharge edges of the impeller vane ends with abrasion-resistant materials, such as ceramics, sintered carbides, etc., in order to extend the life of these parts. However, such ceramics, sintered carbides, and other known hard and abrasion-resisting materials, are inherently brittle, and as a consequence perform very poorly under high impact stresses. Thus, even a small percentage of rebounding material can greatly reduce the effectiveness and life of the abrasion-resisting materials.

It is therefore a primary object of the present invention to provide an improved impeller which will avoid the type of wear which is due to rebounding material impacting upon the impeller vane ends.

Another object is to so design an impeller that it can use, in applicable areas of wear, materials which are resistant to sliding abrasion but not resistant to impact, by protecting these areas from rebound impact.

Another object is to provide an impeller having the foregoing features which can be serviced easily with relatively inexpensive materials.

Still another object is to provide an impeller having the foregoing features that can be readily and simply manufactured.

In summary, in accordance with a preferred form of my present invention, there is provided an improved impeller assembly which incorporates a peripheral ring of spaced-apart loosely supported sleeves made from materials which are resistant to impact type of abrasive wear. These sleeves are so positioned that the particles of material flowing outwardly through the impeller will not come into contact with the sleeves, but the rebounding material will contact and be deflected by the sleeves in such manner that it cannot re-enter the impeller discharge area. More specifically, the sleeves are preferably equally spaced about the periphery of the impeller, vertically disposed between the lower and upper impeller disks, and are spaced sufiiciently far apart to allow the material to be projected outwardly from the impeller Without coming into contact with the sleeves, but close enough together to intercept the arcuate path (relative to the rotating impeller) of the rebounding material, thereby preventing rebounding particles of material from reentering the impeller beyond the centerline circle of the sleeves.

The present invention will be clearly understood from a consideration of the following detailed description of a preferred embodiment illustrated in the drawing in which:

FIG. 1 is a plan view, partly broken away and in section, of an impeller illustrating the improvement of the present invention;

FIG. 2 is an elevational view in section of the impeller of FIG. 1; and

FIG. 3 is a perspective illustration of one of the impeller vanes.

Referring now to the drawing, the impeller 10 comprises an assembly of parts including upper and lower annular discs 12 and 14 which may be secured as by bolts 15 to a hub 16 which is supported on and keyed or otherwise secured to the rotatable shaft 17. Shaft 17 is adapted to be driven at high speed.

Supported above a circular opening in the annular disc 12 is a stationary feed tube 18 through which the particles of material to be reduced in size are fed to the impeller. These particles drop into a cup 19 set in the rotatable hub 16, and when the cup is rotated at high speed the particles of the material quickly fill up the corner areas, as indicated in FIG. 2 of the drawing, forming an inclined surface for the particles of material which follow. All particles are thereafter ejected from the cup 19 into the region between the upper and lower discs 12, 14, of the impeller and are thrown radially outwardly by the impeller vanes by the centrifugal forces resulting from the high speed rotation of the impeller.

The impeller shown in the drawings and now being described, employs an improved type of impeller vane 20. This type of vane 20 is shown, described and claimed in my patent No. 3,162,386, previously referred to. The vane 20 is shown in cross-section in FIG. 1 and in perspective in FIG. 3. It comprises a radially extending arm 21 having bosses 22 and 23 for receiving bolts 15 and 24 for securing the vanes 20 to the upper and lower discs 12, 14 of the impeller assembly. The vane 20 is equipped with two spaced-apart arms 25 and 26 which extend circumferentially forward in the direction of rotation of the impeller, as indicated by the arrow 30. Each of the arms 25, 26 is bent or shaped forward and inward to form what may be termed pockets, as best seen in FIG. 1. A third arm 28 located close to the hub 16 extends inwardly and rearwardly relative to the direction of rotation of the impeller. The function of arm 28 will be referred to later.

Each of the arms 25, 26, and 28 has a height equal to the spacing between the upper and lower discs 12 and 14, and each of the arms has secured to its outer end a renewable notched piece, 35, 36, and 38, respectively, preferably of steel. Bonded to each of the two forwardly extending replaceable notched pieces 35 and 36, is a liner, and 136, respectively. Liners 135 and 136 are made of abrasion resistant material, preferably carbides, ceramics and the like. The steel extensions 35, 36 and the liners 135, 136 are notched at the outward ends, in the manner shown in FIG. 3. Through the notches, identified in the drawing by the reference numerals 35n, 36n and 38n, pass the particles of material as they are projected from the cup 19 toward the outer periphery of the impeller. The fillet-shaped upper and lower edges of the extensions 35,

36, and 38, which define the notches, prevent the projected material from spreading upwardly and downwardly, and thereby prevent the material from coming into high speed contact with the surfaces of the discs 12 and 14. Thus, the disc surfaces are protected against undesirable abrasive Wear.

When the impeller assembly is rotated at high speed in the direction of the arrow 30, the particles of material fed through tube 18 fall into the cup 19, climb up the slope of the bedded material, as illustrated in FIG. 2, are ejected from the cup 19, and are thrown outwardly in the direction of the arrows 31 in FIG. 1. The pockets formed by the arms 25 and 26 and their extensions 35 and 36-, rapidly fill up with lodged particles, as shown in FIG. 1, the innermost pockets filling up first and the outermost pockets filling up thereafter. Thereafter, most of the particles ejected from the cup 19 are channeled through the notches 35n and 36n. These particles follow the path indicated in FIG. 1 by the arrows 32. These lodged particles protect the arms 25 and 26 and their extensions 35 and 36, and prevent wear thereof. Particles which strike particles already lodged in the innermost pocket are thrown back into the channel, and are then carried through the notch 35n of extension 35 of arm 25. If they should strike the bed of lodged particles of the outer pocket they would again be thrown back into the channel stream. It will be seen, then, that the arms 25 and 26 with their notched extensions 35 and 36 function to refocus the particles, in that particles which tend to diverge too widely, either upwardly or downwardly, from the channel path defined by the notches, 35n and 36:4, are caused to return to the region of the channel, i.e., to the region between but not in contact with either the upper or lower discs 12, 14. Thus, the under surface of the upper disc 12 and the upper surface of the lower disc 14 are protected from the abrasive action of the otherwise widely divergent particles and thus the amount of wear on discs 12, 14 is substantially reduced.

The function of the third arm 28, which extends inwardly and rearwardly with respect to the direction of impeller rotation, is to direct particles which are ejected by the cup 19 in the region of the arrow 33 in FIG. 1, into the pocket or channel of the next rearward vane.

The structural arrangement of impeller vane described thus far is described in greater detail in my US. Patent No. 3,162,386. The employment of this type of vane has been found effective to prevent wear of the impeller discs 12 and 14, and also effective to prevent wear on the inner surfaces of vane arms 25 and 26 and their extensions 35 and 36.

It has been found, however, that the particles of material discharged from the impeller along the path indicated by the arrows 32 have a tendency to rebound from the breaker plates, or from the bed of lodged particles of like material on the wall of the impeller bowl, or from whatever other surface the particles are projected against, none of which is illustrated, the extent or degree to which the particles rebound depending more or less upon the clearances between the outer periphery of the impeller and the breaker plates, or bed of like material, or other surface. Those particles which rebound tend to re-enter the impeller discharge area.

Consider now the situation where highly abrasive material is being pulverized. In such instances, the outer surfaces of the impeller vanes tend to wear due to sliding abrasive action of the outwardly projected particles. To reduce the rate of such wear, the prior art has lined the discharge edges of the impeller vane ends with materials which are resistant to sliding abrasion, such sliding abrasion resisting materials being ceramics, sintered carbides, and the like. These materials, while hard and abrasion resistant, are inherently brittle, and, as a consequence, perform very poorly under high impact stresses. Thus, if particles rebound from the breaker plates or other surfaces, into the impeller discharge area, such rebounding particles greatly reduce the effective life of any protective material which is abrasion resistant but not impact resistant. One expedient is to reduce the speed of the impeller, but this solution is obviously unsatisfactory, for while it reduces the impact effect of the rebounds, it also reduces the crushing effect of the pulverizer.

In accordance with the present invention, the solution to the problem is in the provision of a peripheral ring of spaced-apart pins 40 each equipped with a loosely supported sleeve 41 made of material which is resistant to impact type of wear. The pins 40 are so arranged, relative to the vanes 20, that the particles of material being projected outwardly by centrifugal force along the path indicated by the arrows 32 pass between adjacent pins 40 without making contact therewith.

The material which rebounds, rebounds in the direction indicated by the arrows 42. These rebounding particles hit the sleeves 41 and are deflected away from the impeller. Thus, the sleeves 41 prevent the rebounding particles from re-entering into the impeller discharge area, and accordingly the vanes 20 are protected from impact wear. As a consequence, the vane discharge ends may be made of material which is resistant to sliding abrasion, but it need not also be resistant to impact.

The pins 40 are preferably equally spaced about the periphery of the impeller, and are sufliciently close together to intercept the rebounding particles, which follow an arcuate path relative to the rotating impeller.

The sleeves 41 are preferably circular in cross section but may be of any suitable shape so long as dynamic balance is maintained. The sleeves 41 extend between the discs 12 and 14 of the impeller. However, the sleeves are short enough not to be clamped in position by the impeller discs, thereby to permit their replacement by merely punching out the pins 40 without disassembling the impeller. Sleeves 41 are preferably made of resilient or nonbrittle materials such as ordinary steel, synthetic plastics, steel pipe coated with plastics, and other impact resistant materials.

Pins 40 are, in the preferred embodiment, seated in counter drilled holes 43 in the bottom disc 14 and are knurled or upset at the top end to provide a slight drive fit in the upper disc 12. When a sleeve 41 is to be replaced, the pin 40 is merely driven upwardly, as by a suitable punch. Other means of fastening the pins and sleeves may be employed without departing from the present invention.

It will be seen that the present invention permits the vane discharge parts to be formed of materials which are resistant to sliding abrasion without having to be impact resistant. The sleeves 41, on the other hand, are subjected primarily to impact, and may be made of material which is resistant to impact without having to be resistant also to sliding abrasion.

It will be noted that the type of vane 20 employed in my improved impeller cooperates with the peripheral ring of pin-supported sleeves 41 to produce the improvement of the present invention. The material projected from the cup 19, after passing through the inner notch 3511, climbs up the slope of the bed of material in the pocket 126 of the outer arm 26, passes through the outer notch 36n, and is projected outwardly between adjacent pin-supported sleeves 41. The fact that the particles are forced to climb the slope of the bed of material in the pocket 126 reduces the radial velocity of the particles, with the result that the ratio of the peripheral component of velocity to the radial component of velocity of the particles projected from the periphery of the impeller becomes greater than 1. However, it is also to be noted that since the particles are required to move up the inclined surface of the bed of pocket 126 at an angle relative to the radial line of the impeller, this causes the particles to pass through notch 3611 and to be projected from the impeller periphery at an angle which, relative to the radial line of the impeller,

is smaller than would be the case if the particles followed a radial path from the cup 19 to the edge of the impeller. Thus, the particles are ejected from the notch 3611 at an angle which carries them between the adjacent sleeves 41.

Heretofore centrifugal impellers have been devised to incorporate peripheral pins or posts which are either extensions of the impeller vanes or are used as secondary pulverizing means to reduce rebounding particles, similar to that shown in Patent No. 3,155,326 granted to R. E. Rhodes. Pins or posts employed in this manner do not allow the optimum use of materials best adapted for resisting either sliding abrasion or impact abrasion, both types of wear being inherent and found in combination in this type of pulverizer.

While the preferred embodiment of this invention has been described in some detail, it will be obvious to one skilled in the art that various modifications may be made without departing from the invention as hereinafter claimed.

Having described my invention, I claim:

1. In a centrifugal pulverizer for reducing the size of particles of material, an impeller assembly adapted to be rotated at high speed, said impeller assembly including: upper and lower horizontally disposed impeller discs; a plurality of radially disposed impeller vanes vertically secured between said discs, each of said impeller vanes having a generally radial main portion and at least one inwardly cupped arm extending generally circumferentially forward therefrom in the direction of rotation of said impeller assembly forming a pocket for trapping said particles, the extremity of said arm having a lateral notch for passage therethrough of said particles; and a ring of spaced-apart vertical pins between said upper and lower impeller discs and so disposed about the periphery of said impeller that the particles of material moving outwardly through the notch of said cupped arm pass between adjacent pins, said pins being sufliciently closely spaced to prevent particles of material which rebound towards said impeller from passing through said ring, thereby to protect said impeller vanes from impact wear.

2. In a centrifugal pulverizer as claimed in claim 1 characterized in that said pins are provided with sleeves loosely mounted thereon.

3. In a centrifugal pulverizer as claimed in claim 2 further characterized in that said sleeves are of circular cross-section and are formed of impact resistant material.

4. In a centrifugal pulverizer as claimed in claim 3 further characterized in that said pins are equally spaced.

5. In a centrifugal pulverizer as claimed in claim 4 further characterized in that each of said impeller vanes has at least two inwardly cupped arms extending generally circumferentially forward from the radial main portion.

6. In a centrifugal pulverizer as claimed in claim 5 further characterized in that the notched extremities of said cupped arms are removably secured to said arms for replacement purposes.

7. In a centrifugal pulverizer as claimed in claim 6 further characterized in that each of said cupped arms is adapted to trap particles of material to form a bed of lodged particles having a surface which is inclined forwardly and outwardly relative to the radial line of said impeller and adapted to cause following particles to approach the notch in the extremity of said cupped arm at an angle which is inclined forwardly and outwardly relative to the radial line, thereby to cause particles which pass through said notch to be ejected from said impeller at a reduced angle relative to said radial line.

References Cited UNITED STATES PATENTS 0 WILLIAM W. DYER, JR., Primary Examiner.

R. J. ZLOTNIK, Assistant Examiner. 

1. IN A CENTRIFUGAL PULVERIZER FOR REDUCING THE SIZE OF PARTICLES OF MATERIAL, AN IMPELLER ASSEMBLY ADAPTED TO BE ROTATED AT HIGH SPEED, SAID IMPELLER ASSEMBLY INCLUDING: UPPER AND LOWER HORIZONTALLY DISPOSED IMPELLER DISCS; A PLURALITY OF RADIALLY DISPOSED IMPELLER VANES VERTICALLY SECURED BETWEEN SAID DISCS, EACH OF SAID IMPELLER VANES HAVING A GENERALLY RADIAL MAIN PORTION AND AT LEAST ONE INWARDLY CUPPED ARM EXTENDING GENERALLY CIRCUMFERENTIALLY FORWARD THEREFROM IN THE DIRECTION OF ROTATING OF SAID IMPELLER ASSEMBLY FORMING A POCKET FOR TRAPPING SAID PARTICLES, THE EXTERMITY OF SAID ARM HAVING A LATERAL NOTCH FOR PASSAGE THERETHROUGH OF SAID PARTICLES; AND A RING OF SPACED-APART VERTICAL PINS BETWEEN SAID UPPER AND LOWER IMPELLER DISCS AND SO DISPOSED ABOUT THE PERIPHERY OF SAID IMPELLER THAT THE PARTICLES OF MATERIAL MOVING OUTWARDLY THROUGH THE NOTCH OF SAID CUPPED ARM PASS BETWEEN ADJACENT PINS, SAID PINS BEING SUFFICIENTLY CLOSELY SPACED TO PREVENT PARTICLES OF MATERIAL WHICH REBOUND TOWARDS SAID IMPELLER FROM PASSING THROUGH SAID RING, THEREBY TO PROTECT SAID IMPELLER VANES FROM IMPACT WEAR. 